This invention relates to lighting fixtures. More particularly, this invention relates to lighting fixtures utilizing two elongated lamps to produce increased lamp light output density.
One goal of the lighting industry has been to provide luminaires--lighting fixtures with lamps--with ever higher lamp light output densities. Light output density is generally measured in lumens/foot (L/F), a lumen being a unit of luminous flux. For example, a two-foot-long (approximately 0.61-meter--long) lamp that produces 1000 lumens achieves 500 L/F (approximately 1,639 L/Meter)
One manner of providing a higher lamp light output density has been to use high output lamps, which achieve a greater luminous flux (measured in lumens) from the same size lamp. For example, while a typical four-foot-long (approximately 1.22-meter-long), 32 -watt, T8-size, rapid start lamp will produce a luminous flux of 2,950 lumens, for 737 L/F (approximately 2,418 L/M), a typical four-foot-long (approximately 1.22-meter-long), 60-watt, T12-size High Output rapid start lamp will produce a luminous flux of 4,350 lumens, for 1,087 L/F (approximately 3,566 L/M), an increase of approximately 50% in light output density.
Another manner of achieving greater light output density from a given luminaire has been through use of compact fluorescent lamps (CFL), such as twin-tube lamps, which produce a greater number of lumens, at approximately the same wattage, than are produced by larger conventional lamps. For example, while a typical four-foot-long (approximately 1.22-meter-long), 32-watt T8-size, rapid start lamp will produce a luminous flux of 2,950 lumens, for 737 L/F (approximately 2,418 L/M), a typical 16.5"-long (approximately 42-centimeter-long), 39 watt, T5-size rapid start CFL sold by General Electric Co. under the name Biax.RTM. produces a luminous flux of 2,850 lumens, for 2,073 L/F (approximately 6,800 L/M), an increase of approximately 180% in light output density. Similar lamps are sold by Philips, North America under the trademark PL-L.RTM. and by Osram under the trademark Dulux L.RTM..
A higher light output density value for a lighting fixture can be achieved by providing an array of lamps in as small a cross-sectional area as possible. However, attempts to utilize this manner of achieving a greater light output density are inherently constrained by the dimensions of lampholders. For example, the width of a standard 4-pin plug-in compact fluorescent lampholder, which is greater than the width of the lamp it is designed to hold, prevents the light-emitting tubes of the CFL lamps from being placed as close together as desired to produce the greatest lamp light output density, as when two of the lamps are placed essentially side-by-side.
The placement of two lamps side-by-side is desirable for several reasons. First, as suggested above, placement of multiple lamps side-by-side increases the numerator in the L/F calculation, serving to increase the overall value of light output density of a luminaire. For example, two 16.5"-long, 39 watt, twin-tube CFL lamps, placed side-by-side, would produce 5,700 lumens, for 4,145 L/F (approximately 13,540 L/M), an increase of approximately 100% in light output density, as compared to one 16.5"-long, 39 watt, twin-tube CFL lamp, or an increase of 462% over the four-foot-long, 32-watt, T8-size, rapid start lamp described above. Additionally, the light emitted from multiple hairline light sources, when placed adjacent one another, simulates the light that would be emitted from one, larger, hairline light source. As such, the light from the multiple sources is easier to direct and control by conventional reflectors or lenses that are designed for hairline light sources. Commonly used reflectors provide either elliptical or parabolic arcs, or both. For example, a reflector with both elliptical and parabolic arcs is sold by Elliptipar, Inc., of West Haven, Conn., under the trademark ELLIPTIPAR.RTM..
Therefore, it would be desirable to provide an arrangement for orienting multiple elongated lamps in a lighting fixture that allows the placement of the multiple lamps closer together than would normally be allowed by the size of the lampholders.
It would also be desirable to provide an arrangement for orienting multiple elongated lamps in a lighting fixture that allows the placement of the multiple lamps such that they simulate, as closely as possible, a hairline source of light.